Nervous Tissue: Neurons and their synapses
Terms
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- Characteristics of Nervous system
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-Nervous tissue=Neurons and neuroglia cells
-CNS=brain and spinal cord
-PNS=everything else
Neuron
-one cell, structural unit, functional unit
-receives and transmits signals
-chemical and electrical impulses
-have set number of neurons at birth
-do not divide only in olfactory
-can be destroyed - Regions of a Neuron
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-Input or dendritic zone receives excitation
-Output or telodendritic zone transfers excitation
-axon cnducts excitation
-cell body or perikaryon located within dendritic zone in multipolar neurons or is associated with axon in unipolar and bipolar and is the housekeeper - Anatomical Classification
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Unipolar
-perikaryon has single axon that divides into a peripheral branch and central branch
-efferent in nature
-touching and taste
Bipolar
-have 2 processes and are afferent in nature
-perikaryon can be located within axon or at junction of axon and single dendrite
-vision, hearing, smell
Mulitpolar
-Perikaryon several dendrites and one axon
-type I long axon and type II short axon
-all motor neurons, and in brain and spinal cord - Neuron Structure
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-Variety of shapes and sizes
-larger processes=larger cell body
-faster transmission=larger axon and larger cell body
-dendritic zone has ligand-reactive receptors
-axon membrane contains voltage gated Na channels
-bulbs have voltage-gated Ca channels and receptors for neurotransmitter reuptake - Neurons need
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-proteins (microfilaments)
-Prominent rER and free ribosomes
-Nissl's substance
-prominent nucleus - Perikaryon characteristics
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-has axon hillock
Nucleus
-size proportional to neuron size
-euchromatic in larger neurons
-prominent nucleus
-spherical in shape and centrally located in somatic, peripheral in autonomous
Cytoplasm
-high protein synthesis
-Nissl's substance, in dendrites, not in hillock
-prominent Golgi
-microtubules and neurofilaments
-secretory vesicles are transported to bulbs
-lipofuscin pigment granules - cont'd
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Dendrites
-highly branched, designed to receive synaptic contacts
-trunks have organelles
-smaller branches have microtubules, neurofilaments, mitochondria and sER
-spines: short expanded processes attached to dendritic branch by narrow stalk
-synaptic site electron dense
Axons
-long cylindrical process originatin from axon hillock and ending at highly-branched telodendrites and bulbs
-sparse collateral branching
-microtubules, neurofilaments,mitochondria and sER
-lack rER
-rapid retrograde
-myelinated increase conduction speed - Telodendrites
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-end in terminal expansions
-proteins from cell body packaged in sER of telo. and stored
-release neurotransmitters
-clustering of synaptic vesicles occurs by actin filaments - Neuronal Communication
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-communicate with each other, muscles, and glands
-gap junctions are rare among neurons
-neuronal communication by nitric oxide gas occurs b/c it can pass freely throufh neuronal membrane and inhibit neurotransmitter release
-interneuronal chemical synapses are the most common, btw neurons, muscles or glands - Interneuronal Chemical Synapse
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-Neurotransmitters are biogenc amines
-excitatiry and inhibitory receptors
-receptors determine action
-gltamate is associated with excitatory synapses
-glycine is associated with inhibitory synapses
-synapses are mostly axosomatic and axodendritic
-cell body affects membrane potential at nearby initial segment of axon
-relative infulence of a neuron on another depends on number of synapses and where the synapse is made - Ultrastructure of Synapse
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Presynaptic element
-bulb next to postsynaptic
-synaptic vesicles
-electron dense
Synaptic cleft
-20-30 nm wide
-proteins hold membranes together
Postsynaptic membrane
-electron dense membrane
-receptor - Physiology
- see hand out for steps